Adaptive Strategies of Desert Shrub Stem–Leaf Anatomical Traits in the High-Altitude Qaidam Basin

High-altitude arid regions are characterized by concurrent water scarcity, low temperatures, and intense solar radiation. However, the adaptive mechanisms of desert shrubs to these combined stressors remain poorly understood. To address this gap, we integrated large-scale field surveys with laboratory measurements of eight stem and leaf anatomical traits across six common desert shrub species in the Qaidam Basin. Principal component analysis (PCA) revealed two primary axes of trait variation. The first principal component (PC1) characterized a trade-off between leaf protective traits (e.g., cuticle and epidermal thickness) and stem hydraulic-storage traits (e.g., central cylinder, xylem, and pith diameters). The second principal component (PC2) was primarily loaded by stem cortex thickness, representing a physiological buffering mechanism. Based on PC1, species were categorized into two distinct strategic groups. Group A prioritized investment in stem conductive and storage tissues, enhancing hydraulic safety under hotter, high-evaporative demand conditions. Conversely, Group B exhibited reinforced leaf protective structures, consistent with tolerance to high radiation and low-temperature stress at higher elevations. The environmental gradients were the primary drivers of this divergence: Group A was associated with aridity, whereas Group B was correlated with elevation. Our findings demonstrate that desert shrubs in the Qaidam Basin have employed diverse adaptive strategies via the modulation of organ-specific anatomical traits to mitigate environmental stressors. These findings offer valuable insights into plant adaptive mechanisms, with implications for predicting vegetation responses and informing ecological restoration in high-altitude arid ecosystems.